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Linux/arch/mips/kernel/kprobes.c

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  1 /*
  2  *  Kernel Probes (KProbes)
  3  *  arch/mips/kernel/kprobes.c
  4  *
  5  *  Copyright 2006 Sony Corp.
  6  *  Copyright 2010 Cavium Networks
  7  *
  8  *  Some portions copied from the powerpc version.
  9  *
 10  *   Copyright (C) IBM Corporation, 2002, 2004
 11  *
 12  *  This program is free software; you can redistribute it and/or modify
 13  *  it under the terms of the GNU General Public License as published by
 14  *  the Free Software Foundation; version 2 of the License.
 15  *
 16  *  This program is distributed in the hope that it will be useful,
 17  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 18  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 19  *  GNU General Public License for more details.
 20  *
 21  *  You should have received a copy of the GNU General Public License
 22  *  along with this program; if not, write to the Free Software
 23  *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 24  */
 25 
 26 #include <linux/kprobes.h>
 27 #include <linux/preempt.h>
 28 #include <linux/uaccess.h>
 29 #include <linux/kdebug.h>
 30 #include <linux/slab.h>
 31 
 32 #include <asm/ptrace.h>
 33 #include <asm/branch.h>
 34 #include <asm/break.h>
 35 
 36 #include "probes-common.h"
 37 
 38 static const union mips_instruction breakpoint_insn = {
 39         .b_format = {
 40                 .opcode = spec_op,
 41                 .code = BRK_KPROBE_BP,
 42                 .func = break_op
 43         }
 44 };
 45 
 46 static const union mips_instruction breakpoint2_insn = {
 47         .b_format = {
 48                 .opcode = spec_op,
 49                 .code = BRK_KPROBE_SSTEPBP,
 50                 .func = break_op
 51         }
 52 };
 53 
 54 DEFINE_PER_CPU(struct kprobe *, current_kprobe);
 55 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
 56 
 57 static int __kprobes insn_has_delayslot(union mips_instruction insn)
 58 {
 59         return __insn_has_delay_slot(insn);
 60 }
 61 
 62 /*
 63  * insn_has_ll_or_sc function checks whether instruction is ll or sc
 64  * one; putting breakpoint on top of atomic ll/sc pair is bad idea;
 65  * so we need to prevent it and refuse kprobes insertion for such
 66  * instructions; cannot do much about breakpoint in the middle of
 67  * ll/sc pair; it is upto user to avoid those places
 68  */
 69 static int __kprobes insn_has_ll_or_sc(union mips_instruction insn)
 70 {
 71         int ret = 0;
 72 
 73         switch (insn.i_format.opcode) {
 74         case ll_op:
 75         case lld_op:
 76         case sc_op:
 77         case scd_op:
 78                 ret = 1;
 79                 break;
 80         default:
 81                 break;
 82         }
 83         return ret;
 84 }
 85 
 86 int __kprobes arch_prepare_kprobe(struct kprobe *p)
 87 {
 88         union mips_instruction insn;
 89         union mips_instruction prev_insn;
 90         int ret = 0;
 91 
 92         insn = p->addr[0];
 93 
 94         if (insn_has_ll_or_sc(insn)) {
 95                 pr_notice("Kprobes for ll and sc instructions are not"
 96                           "supported\n");
 97                 ret = -EINVAL;
 98                 goto out;
 99         }
100 
101         if ((probe_kernel_read(&prev_insn, p->addr - 1,
102                                 sizeof(mips_instruction)) == 0) &&
103                                 insn_has_delayslot(prev_insn)) {
104                 pr_notice("Kprobes for branch delayslot are not supported\n");
105                 ret = -EINVAL;
106                 goto out;
107         }
108 
109         if (__insn_is_compact_branch(insn)) {
110                 pr_notice("Kprobes for compact branches are not supported\n");
111                 ret = -EINVAL;
112                 goto out;
113         }
114 
115         /* insn: must be on special executable page on mips. */
116         p->ainsn.insn = get_insn_slot();
117         if (!p->ainsn.insn) {
118                 ret = -ENOMEM;
119                 goto out;
120         }
121 
122         /*
123          * In the kprobe->ainsn.insn[] array we store the original
124          * instruction at index zero and a break trap instruction at
125          * index one.
126          *
127          * On MIPS arch if the instruction at probed address is a
128          * branch instruction, we need to execute the instruction at
129          * Branch Delayslot (BD) at the time of probe hit. As MIPS also
130          * doesn't have single stepping support, the BD instruction can
131          * not be executed in-line and it would be executed on SSOL slot
132          * using a normal breakpoint instruction in the next slot.
133          * So, read the instruction and save it for later execution.
134          */
135         if (insn_has_delayslot(insn))
136                 memcpy(&p->ainsn.insn[0], p->addr + 1, sizeof(kprobe_opcode_t));
137         else
138                 memcpy(&p->ainsn.insn[0], p->addr, sizeof(kprobe_opcode_t));
139 
140         p->ainsn.insn[1] = breakpoint2_insn;
141         p->opcode = *p->addr;
142 
143 out:
144         return ret;
145 }
146 
147 void __kprobes arch_arm_kprobe(struct kprobe *p)
148 {
149         *p->addr = breakpoint_insn;
150         flush_insn_slot(p);
151 }
152 
153 void __kprobes arch_disarm_kprobe(struct kprobe *p)
154 {
155         *p->addr = p->opcode;
156         flush_insn_slot(p);
157 }
158 
159 void __kprobes arch_remove_kprobe(struct kprobe *p)
160 {
161         if (p->ainsn.insn) {
162                 free_insn_slot(p->ainsn.insn, 0);
163                 p->ainsn.insn = NULL;
164         }
165 }
166 
167 static void save_previous_kprobe(struct kprobe_ctlblk *kcb)
168 {
169         kcb->prev_kprobe.kp = kprobe_running();
170         kcb->prev_kprobe.status = kcb->kprobe_status;
171         kcb->prev_kprobe.old_SR = kcb->kprobe_old_SR;
172         kcb->prev_kprobe.saved_SR = kcb->kprobe_saved_SR;
173         kcb->prev_kprobe.saved_epc = kcb->kprobe_saved_epc;
174 }
175 
176 static void restore_previous_kprobe(struct kprobe_ctlblk *kcb)
177 {
178         __this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
179         kcb->kprobe_status = kcb->prev_kprobe.status;
180         kcb->kprobe_old_SR = kcb->prev_kprobe.old_SR;
181         kcb->kprobe_saved_SR = kcb->prev_kprobe.saved_SR;
182         kcb->kprobe_saved_epc = kcb->prev_kprobe.saved_epc;
183 }
184 
185 static void set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
186                                struct kprobe_ctlblk *kcb)
187 {
188         __this_cpu_write(current_kprobe, p);
189         kcb->kprobe_saved_SR = kcb->kprobe_old_SR = (regs->cp0_status & ST0_IE);
190         kcb->kprobe_saved_epc = regs->cp0_epc;
191 }
192 
193 /**
194  * evaluate_branch_instrucion -
195  *
196  * Evaluate the branch instruction at probed address during probe hit. The
197  * result of evaluation would be the updated epc. The insturction in delayslot
198  * would actually be single stepped using a normal breakpoint) on SSOL slot.
199  *
200  * The result is also saved in the kprobe control block for later use,
201  * in case we need to execute the delayslot instruction. The latter will be
202  * false for NOP instruction in dealyslot and the branch-likely instructions
203  * when the branch is taken. And for those cases we set a flag as
204  * SKIP_DELAYSLOT in the kprobe control block
205  */
206 static int evaluate_branch_instruction(struct kprobe *p, struct pt_regs *regs,
207                                         struct kprobe_ctlblk *kcb)
208 {
209         union mips_instruction insn = p->opcode;
210         long epc;
211         int ret = 0;
212 
213         epc = regs->cp0_epc;
214         if (epc & 3)
215                 goto unaligned;
216 
217         if (p->ainsn.insn->word == 0)
218                 kcb->flags |= SKIP_DELAYSLOT;
219         else
220                 kcb->flags &= ~SKIP_DELAYSLOT;
221 
222         ret = __compute_return_epc_for_insn(regs, insn);
223         if (ret < 0)
224                 return ret;
225 
226         if (ret == BRANCH_LIKELY_TAKEN)
227                 kcb->flags |= SKIP_DELAYSLOT;
228 
229         kcb->target_epc = regs->cp0_epc;
230 
231         return 0;
232 
233 unaligned:
234         pr_notice("%s: unaligned epc - sending SIGBUS.\n", current->comm);
235         force_sig(SIGBUS, current);
236         return -EFAULT;
237 
238 }
239 
240 static void prepare_singlestep(struct kprobe *p, struct pt_regs *regs,
241                                                 struct kprobe_ctlblk *kcb)
242 {
243         int ret = 0;
244 
245         regs->cp0_status &= ~ST0_IE;
246 
247         /* single step inline if the instruction is a break */
248         if (p->opcode.word == breakpoint_insn.word ||
249             p->opcode.word == breakpoint2_insn.word)
250                 regs->cp0_epc = (unsigned long)p->addr;
251         else if (insn_has_delayslot(p->opcode)) {
252                 ret = evaluate_branch_instruction(p, regs, kcb);
253                 if (ret < 0) {
254                         pr_notice("Kprobes: Error in evaluating branch\n");
255                         return;
256                 }
257         }
258         regs->cp0_epc = (unsigned long)&p->ainsn.insn[0];
259 }
260 
261 /*
262  * Called after single-stepping.  p->addr is the address of the
263  * instruction whose first byte has been replaced by the "break 0"
264  * instruction.  To avoid the SMP problems that can occur when we
265  * temporarily put back the original opcode to single-step, we
266  * single-stepped a copy of the instruction.  The address of this
267  * copy is p->ainsn.insn.
268  *
269  * This function prepares to return from the post-single-step
270  * breakpoint trap. In case of branch instructions, the target
271  * epc to be restored.
272  */
273 static void __kprobes resume_execution(struct kprobe *p,
274                                        struct pt_regs *regs,
275                                        struct kprobe_ctlblk *kcb)
276 {
277         if (insn_has_delayslot(p->opcode))
278                 regs->cp0_epc = kcb->target_epc;
279         else {
280                 unsigned long orig_epc = kcb->kprobe_saved_epc;
281                 regs->cp0_epc = orig_epc + 4;
282         }
283 }
284 
285 static int __kprobes kprobe_handler(struct pt_regs *regs)
286 {
287         struct kprobe *p;
288         int ret = 0;
289         kprobe_opcode_t *addr;
290         struct kprobe_ctlblk *kcb;
291 
292         addr = (kprobe_opcode_t *) regs->cp0_epc;
293 
294         /*
295          * We don't want to be preempted for the entire
296          * duration of kprobe processing
297          */
298         preempt_disable();
299         kcb = get_kprobe_ctlblk();
300 
301         /* Check we're not actually recursing */
302         if (kprobe_running()) {
303                 p = get_kprobe(addr);
304                 if (p) {
305                         if (kcb->kprobe_status == KPROBE_HIT_SS &&
306                             p->ainsn.insn->word == breakpoint_insn.word) {
307                                 regs->cp0_status &= ~ST0_IE;
308                                 regs->cp0_status |= kcb->kprobe_saved_SR;
309                                 goto no_kprobe;
310                         }
311                         /*
312                          * We have reentered the kprobe_handler(), since
313                          * another probe was hit while within the handler.
314                          * We here save the original kprobes variables and
315                          * just single step on the instruction of the new probe
316                          * without calling any user handlers.
317                          */
318                         save_previous_kprobe(kcb);
319                         set_current_kprobe(p, regs, kcb);
320                         kprobes_inc_nmissed_count(p);
321                         prepare_singlestep(p, regs, kcb);
322                         kcb->kprobe_status = KPROBE_REENTER;
323                         if (kcb->flags & SKIP_DELAYSLOT) {
324                                 resume_execution(p, regs, kcb);
325                                 restore_previous_kprobe(kcb);
326                                 preempt_enable_no_resched();
327                         }
328                         return 1;
329                 } else if (addr->word != breakpoint_insn.word) {
330                         /*
331                          * The breakpoint instruction was removed by
332                          * another cpu right after we hit, no further
333                          * handling of this interrupt is appropriate
334                          */
335                         ret = 1;
336                 }
337                 goto no_kprobe;
338         }
339 
340         p = get_kprobe(addr);
341         if (!p) {
342                 if (addr->word != breakpoint_insn.word) {
343                         /*
344                          * The breakpoint instruction was removed right
345                          * after we hit it.  Another cpu has removed
346                          * either a probepoint or a debugger breakpoint
347                          * at this address.  In either case, no further
348                          * handling of this interrupt is appropriate.
349                          */
350                         ret = 1;
351                 }
352                 /* Not one of ours: let kernel handle it */
353                 goto no_kprobe;
354         }
355 
356         set_current_kprobe(p, regs, kcb);
357         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
358 
359         if (p->pre_handler && p->pre_handler(p, regs)) {
360                 /* handler has already set things up, so skip ss setup */
361                 reset_current_kprobe();
362                 preempt_enable_no_resched();
363                 return 1;
364         }
365 
366         prepare_singlestep(p, regs, kcb);
367         if (kcb->flags & SKIP_DELAYSLOT) {
368                 kcb->kprobe_status = KPROBE_HIT_SSDONE;
369                 if (p->post_handler)
370                         p->post_handler(p, regs, 0);
371                 resume_execution(p, regs, kcb);
372                 preempt_enable_no_resched();
373         } else
374                 kcb->kprobe_status = KPROBE_HIT_SS;
375 
376         return 1;
377 
378 no_kprobe:
379         preempt_enable_no_resched();
380         return ret;
381 
382 }
383 
384 static inline int post_kprobe_handler(struct pt_regs *regs)
385 {
386         struct kprobe *cur = kprobe_running();
387         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
388 
389         if (!cur)
390                 return 0;
391 
392         if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
393                 kcb->kprobe_status = KPROBE_HIT_SSDONE;
394                 cur->post_handler(cur, regs, 0);
395         }
396 
397         resume_execution(cur, regs, kcb);
398 
399         regs->cp0_status |= kcb->kprobe_saved_SR;
400 
401         /* Restore back the original saved kprobes variables and continue. */
402         if (kcb->kprobe_status == KPROBE_REENTER) {
403                 restore_previous_kprobe(kcb);
404                 goto out;
405         }
406         reset_current_kprobe();
407 out:
408         preempt_enable_no_resched();
409 
410         return 1;
411 }
412 
413 static inline int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
414 {
415         struct kprobe *cur = kprobe_running();
416         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
417 
418         if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
419                 return 1;
420 
421         if (kcb->kprobe_status & KPROBE_HIT_SS) {
422                 resume_execution(cur, regs, kcb);
423                 regs->cp0_status |= kcb->kprobe_old_SR;
424 
425                 reset_current_kprobe();
426                 preempt_enable_no_resched();
427         }
428         return 0;
429 }
430 
431 /*
432  * Wrapper routine for handling exceptions.
433  */
434 int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
435                                        unsigned long val, void *data)
436 {
437 
438         struct die_args *args = (struct die_args *)data;
439         int ret = NOTIFY_DONE;
440 
441         switch (val) {
442         case DIE_BREAK:
443                 if (kprobe_handler(args->regs))
444                         ret = NOTIFY_STOP;
445                 break;
446         case DIE_SSTEPBP:
447                 if (post_kprobe_handler(args->regs))
448                         ret = NOTIFY_STOP;
449                 break;
450 
451         case DIE_PAGE_FAULT:
452                 /* kprobe_running() needs smp_processor_id() */
453                 preempt_disable();
454 
455                 if (kprobe_running()
456                     && kprobe_fault_handler(args->regs, args->trapnr))
457                         ret = NOTIFY_STOP;
458                 preempt_enable();
459                 break;
460         default:
461                 break;
462         }
463         return ret;
464 }
465 
466 /*
467  * Function return probe trampoline:
468  *      - init_kprobes() establishes a probepoint here
469  *      - When the probed function returns, this probe causes the
470  *        handlers to fire
471  */
472 static void __used kretprobe_trampoline_holder(void)
473 {
474         asm volatile(
475                 ".set push\n\t"
476                 /* Keep the assembler from reordering and placing JR here. */
477                 ".set noreorder\n\t"
478                 "nop\n\t"
479                 ".global kretprobe_trampoline\n"
480                 "kretprobe_trampoline:\n\t"
481                 "nop\n\t"
482                 ".set pop"
483                 : : : "memory");
484 }
485 
486 void kretprobe_trampoline(void);
487 
488 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
489                                       struct pt_regs *regs)
490 {
491         ri->ret_addr = (kprobe_opcode_t *) regs->regs[31];
492 
493         /* Replace the return addr with trampoline addr */
494         regs->regs[31] = (unsigned long)kretprobe_trampoline;
495 }
496 
497 /*
498  * Called when the probe at kretprobe trampoline is hit
499  */
500 static int __kprobes trampoline_probe_handler(struct kprobe *p,
501                                                 struct pt_regs *regs)
502 {
503         struct kretprobe_instance *ri = NULL;
504         struct hlist_head *head, empty_rp;
505         struct hlist_node *tmp;
506         unsigned long flags, orig_ret_address = 0;
507         unsigned long trampoline_address = (unsigned long)kretprobe_trampoline;
508 
509         INIT_HLIST_HEAD(&empty_rp);
510         kretprobe_hash_lock(current, &head, &flags);
511 
512         /*
513          * It is possible to have multiple instances associated with a given
514          * task either because an multiple functions in the call path
515          * have a return probe installed on them, and/or more than one return
516          * return probe was registered for a target function.
517          *
518          * We can handle this because:
519          *     - instances are always inserted at the head of the list
520          *     - when multiple return probes are registered for the same
521          *       function, the first instance's ret_addr will point to the
522          *       real return address, and all the rest will point to
523          *       kretprobe_trampoline
524          */
525         hlist_for_each_entry_safe(ri, tmp, head, hlist) {
526                 if (ri->task != current)
527                         /* another task is sharing our hash bucket */
528                         continue;
529 
530                 if (ri->rp && ri->rp->handler)
531                         ri->rp->handler(ri, regs);
532 
533                 orig_ret_address = (unsigned long)ri->ret_addr;
534                 recycle_rp_inst(ri, &empty_rp);
535 
536                 if (orig_ret_address != trampoline_address)
537                         /*
538                          * This is the real return address. Any other
539                          * instances associated with this task are for
540                          * other calls deeper on the call stack
541                          */
542                         break;
543         }
544 
545         kretprobe_assert(ri, orig_ret_address, trampoline_address);
546         instruction_pointer(regs) = orig_ret_address;
547 
548         kretprobe_hash_unlock(current, &flags);
549 
550         hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
551                 hlist_del(&ri->hlist);
552                 kfree(ri);
553         }
554         /*
555          * By returning a non-zero value, we are telling
556          * kprobe_handler() that we don't want the post_handler
557          * to run (and have re-enabled preemption)
558          */
559         return 1;
560 }
561 
562 int __kprobes arch_trampoline_kprobe(struct kprobe *p)
563 {
564         if (p->addr == (kprobe_opcode_t *)kretprobe_trampoline)
565                 return 1;
566 
567         return 0;
568 }
569 
570 static struct kprobe trampoline_p = {
571         .addr = (kprobe_opcode_t *)kretprobe_trampoline,
572         .pre_handler = trampoline_probe_handler
573 };
574 
575 int __init arch_init_kprobes(void)
576 {
577         return register_kprobe(&trampoline_p);
578 }
579 

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